It's got "Coming Soon" slapped on it, so hopefully news of more content for the sequel is already prepped. It's out this Friday in the UK.
It's not a viral campaign for Left 4 Dead 2 itself, as what would be the point now? It's out already via Steam and in the US, with Europe and the UK getting it in shops tomorrow. We've been honing our survivalist nature already, and jotted down some diary notes.
Whatever this teaser site has in store for us, it'll be here "soon".